A wiper apparatus is equipped with a wiper pivot shaft (shaft). The intermediate portion of the shaft is inserted into a pivot holder so that the shaft is rotatable supported. The pivot holder is fixed onto a vehicle body. A link lever is attached to one end portion of the shaft, while a wiper arm is attached to the other end portion of the shaft. A motor is connected to the link lever via a link mechanism, and a wiper blade is retained on the wiper arm. The link mechanism converts the rotary motion of the motor to the reciprocatively rotational motion (swinging motion) of the link lever. A reciprocatively rotational torque is transmitted to the shaft through the reciprocative rotation of the link lever, so that the shaft causes the wiper arm to reciprocatively rotate (swing) along a glass surface. As the wiper arm reciprocatively rotates, the wiper blade wipes the glass surface.
As shown in FIG. 9(A), a first end portion 102 of a shaft 100 has a smaller diameter and serves as a link-lever-attaching portion. A step 106 is formed between the first end portion 102 and an intermediate portion 104. The outer circumferential surface of the one end portion 102 is knurled. An engagement hole 110 is formed in a link lever 108 at one end portion thereof. As shown in FIG. 9(B), the link lever 108 is driven onto the first end portion 102 of the shaft 100, and the first end portion 102 is press-fitted into the engagement hole 110 until the hole edge portion of the link lever 108 abuts the step 106. After the press fit, the tip end of the first end portion 102 projecting from the engagement hole 110 is crimped (the crimped portion is denoted by numeral 112). Thus, the link lever 108 is attached to the one end portion 102 of the shaft 100.
Such a configuration is made public in Japanese Utility Model Application Laid-Open Nos. 4-113262, 4-113263, and 4-113264.
A large load is expected to be imposed on the wiper arm. The link lever 108 needs to obtain such an anti-slip torque (joining force) as not to slip with respect to the one end portion 102 of the shaft 100 within the expected range of load. A slip disables a wiper.
When the anti-slip torque is compared between different diameters A (knurl diameters A) of the one end portion 102 of the shaft 100, it is found that the larger the knurl diameter A is, the larger anti-slip torque is obtained. The knurl diameter A is set according to a required anti-slip torque.
On the other hand, when the step 106 located between the intermediate portion 104 and the first end portion 102 is small, the surface of contact between the step 106 and the link lever 108 becomes small. When the contact surface is small, the hole edge portion of the engagement hole 110 of the link lever 108 bites the intermediate portion 104 of the shaft 100 upon press fit of the link lever 108. As a result of this bite, the length of the intermediate portion 104 of the shaft 100 becomes short, and consequently the installed position of the link lever 108 becomes different from an expected position. That is, after the link lever 108 is press-fitted, the axial dimension of the shaft 100 is in danger of becoming different than what it was before the press-fitting. Further, for assemblies of the shaft 100 and the link lever 108 obtained by press-fitting the shaft 100 into the link lever 108, the amount of the link lever 108 biting the intermediate portion 104 may differ, resulting in potential variations in the axial dimension of the shaft 100.
Thus, the step 106 must have such a size as to prevent such a problem.
However, when the knurl diameter A to be set is large, the diameter B of the intermediate portion 104 of the shaft 100 must also be made large; otherwise, the step 106 having a required size will not be secured. When the diameter B of the intermediate portion 104 of the shaft 100 is made large in order to secure the step 106 having a required size, the diameter B becomes unnecessarily large. As a result, the shaft 100 is unnecessarily overweighted at the intermediate portion 104 and is also unnecessarily strengthened.
As shown in FIG. 10, when the step 106 is small, the step 106 fails to receive the link lever 108 in a proper posture upon press fit of the link lever 108, so that there arises a misalignment between the axis of the shaft 100 and the axis of the engagement hole 110. Thus, the link lever 108 fails to assume the posture represented by a solid line in FIG. 10, and inclines as represented by a two-dot-and dash line in FIG. 10, resulting in impaired perpendicularity of an angle .theta. between the link lever 108 and the shaft 100. When perpendicularity of the angle .theta. is impaired, the axis of the shaft 100 does not become parallel to the axis of a pivot 118, which is provided at an end portion of the link lever 108 opposed to the engagement hole 110 and is connected to the aforementioned link mechanism so as to reciprocatively rotate the link lever 108. Thus, as the link lever 108 rotates reciprocatively, there occurs an uneven sliding contact between one opening end of a pivot holder 114, into which the intermediate portion of the shaft 100 is inserted, and the link lever 108 opposed thereto. When this uneven sliding contact occurs, the anti-slide torque becomes unstable, and the thrust play of the shaft 100 also becomes unstable.
Also, when the link lever 108 inclines as represented by the two-dot-and-dash line in FIG. 10 with a resultant impairment of perpendicularity of the angle .theta., there becomes unstable a dimension L between a mating surface 117 for attachment to a vehicle body of an attachment flange 116, which is formed on the periphery of the pivot holder 114 in order to fix the pivot holder 114 onto the vehicle body, and a pivotal point 119 of the pivot 118 of the link liver 108, resulting in a failure to obtain a predetermined wiping angle of a wiper arm 108.
Thus, a plain washer 120 and a wave washer 122 are interposed between the pivot holder 114 and the link lever 108 so as to stabilize the anti-slip torque and the thrust play of the shaft 100.
Japanese Utility Model Publication No. 3011446 introduces a shaft having a flange portion which contacts a link lever. However, the relation between the flange portion and a pivot holder is not considered at all.